The present invention relates to a method of measuring the dimensions and the alignment of a thin film magnetic head which comprises a magnetic induction type conversion element or a magnetoresistance effect element and which is formed on a substrate by a lamination process, and wherein the method employs a dimension and alignment measuring apparatus; and, more specifically, the invention relates to a method of measuring the dimensions and the alignment of a magnetoresistance effect element with a high degree of accuracy, and an apparatus for carrying out the method.
Lately, in magnetic disk apparatuses, there has been a steady trend toward reduction in the size and enlargement in the capacity thereof; and, currently, small size magnetic disk apparatuses equipped with a 3.5 inch or 2.5 inch disk have become mainstream items. In such small size magnetic disk apparatuses, since the rotation speed of the disk is relatively low, a decrease in the reproduced output has become a great concern in the use of a magnetic induction type head whose reproduced output is dependent on the disk speed.
In contrast to this, a magnetoresistance effect type head (hereinafter referred to as an MR head : MR=magneto-resistive) that employs a magnetoresistance effect element (hereinafter referred to as an MR element) whose resistance varies in accordance with a change in the magnetic field produces an output that is not dependent on the speed of the disk, and, hence, such a head can produce a high reproduced output even in the case of a small size magnetic disk apparatus.
Besides, since the MR heads can deliver a higher reproduced output compared to magnetic induction type magnetic heads, even when applied to narrower tracks, which is accompanied by a higher-density storage configuration, the MR heads are considered to be suitable to satisfy the trend toward miniaturization and mass storage in the magnetic media.
By the way, since an MR head detects a change in the resistance value caused by a change in the magnetic field, an MR head that uses an MR element exposed in a plane of a magnetic head slider opposed to the disk (hereinafter referred to as a floating surface) has a larger reproduction efficiency. In such an MR head, whose MR element is exposed in the floating plane thereof, part of the MR element is processed (lapped and polished, hereinafter referred to only as being lapped for simplicity) so as to expose the MR element in the floating plane in processing the floating plane. The dimension in a direction normal to the floating plane of the MR element is called the height of the MR element (hMR), which is controlled so as to be within a prescribed value by controlling the amount of lapping in a lapping process.
In the MR head, the reproduced output changes depending on the height of the MR element, and, hence, a problem that the reproduced output varies or the reproduced output cannot reach a prescribed level may occur if the heights of the MR elements vary. Therefore, to prevent a variation in the reproduced output of the MR head and also to attain a high yield in the manufacture thereof, it is necessary to control the heights of the MR elements with a high degree of accuracy in the lapping process. For example, in the case of a surface recording density of 4 Gbit/inch2, presumably the accuracy of the height of the MR element is required to be about xc2x10.2 gm; whereas, in the case of a surface recording density of 10 Gbit/inch2, the accuracy is required to be about xc2x10.15 gm.
In order to control the heights of the MR elements with a high degree of accuracy in the lapping process, it is important to measure the heights of the MR elements accurately during the lapping. Presently, the design height of an MR element is about 0.5 to 3 gm. Since an induction type head for writing data is formed on the top of the MR element, it is difficult to directly measure the height of the MR element with optical means.
With this in view, Japanese Patent Laid-open Publication Nos. 63-34713 and 2-29913 propose a method wherein the height of the MR element (or the amount of lapping in the lapping process) is measured indirectly by a method wherein a measurement marker is formed in an element formation process and measurements are made based on the marker using optical means. However, this method can hardly be applied to in-process measurement during the lapping process.
Now, a method is proposed as a feasible method to perform in-process measurement wherein the resistance value of the MR element is measured and then the value is converted to the height of the MR element. This method can be implemented by two techniques: one is described in Japanese Patent Laid-Open Publication No. 5-46945, and proposes to directly measure the resistance value of the MR element itself and convert the value to the height of the MR element; and the other is described in Japanese Patent Laid-open-Publication No. 63-191570, and proposes to measure the resistance of an element (hereinafter referred to as resistance detector element (ELG element; ELG=Electric Lapping Guide)) that is formed separately from the MR element and to calculate the height of the MR element from the resistance value.
Of these methods, the former method for directly measuring the resistance of the MR element has the following problems.
(1) The MR element is formed using a thin film technology whose typical techniques are sputtering, exposure, ion-milling, etc. The dimensional accuracy attainable through this process is about xc2x10.2 xcexcm. On the other hand, the width of the MR element (i.e., track width) is as narrow as 0.8 to 2.0 xcexcm, and, therefore, a variation in the resistance value of the MR element occurs due to a variation in the track width.
(2) In forming an MR film by sputtering, there occurs a variation in its thickness depending on its position on a wafer, namely whether it is at a center part or an edge part of the wafer, and the variation in the thickness in the wafer becomes a factor which contributes to the variation in the resistance value of individual MR elements. Especially, in recent years, the film thickness of the MR element has become thinner, and so the unevenness of the film thickness tends to increase. As a result, the variation in the resistance value also increases. That is, a real MR element suffers from a variation in the resistance value due to a variation in the track width and an unevenness in the film thickness. This variation in the resistance value causes an error in measuring the height of the MR element, hence becoming one of the factors responsible for deterioration of the accuracy of the measurement.
In contrast to this, the latter method for performing in-process measurement by measuring the resistance value and converting the value to the height of the MR element has the following merits.
(1) In a resistance detector element, the track width can be made larger (10 to 500 gm) arbitrarily, and, therefore, its resistance value hardly varies at all, even when the track width varies by xc2x10.2 xcexcm, for example. Therefore, the variation in the track width has only a little effect on the resistance value.
(2) In a resistance detector element, it is possible to cancel out the unevenness of the film thickness in calculating the height of the MR element from the resistance value of the resistance detector element by the use of a reference pattern element (reference resistance).
As described in the foregoing, the method of performing a measurement of the height of the MR element by the use of a resistance detector element enables in-process measurement of the height of the MR element with a high degree of accuracy, because the effect of both the variation in the track width and the unevenness of the film thickness can be reduced. However, this method involves the following problems.
Both the resistance detector element and the MR element are formed by a thin film process whose typical techniques are sputtering, exposure, ion-milling, etc. In an exposure process, however, when there is an unevenness in the resist film thickness and an illuminance unevenness, a variation in the exposure occurs, and, hence, a variation in dimension results. Further, in some cases, when there is image distortion in the exposure equipment, an alignment error in the element occurs. In the method using a resistance detector element, the real height of the MR element is not directly measured, and it is assumed as a major premise that the resistance detector element and the MR element are formed in conformity to design dimensions and design alignment.
Accordingly, if the dimensions of the resistance detector element and the MR element vary, as described above, or there occurs a misalignment in these elements, such variation and misalignment all give rise to measurement errors, and, finally, a variation in the height of the MR element occurs in the lapping process.
An object of the present invention is to provide a method of in-process measurement of the height of an MR element, wherein the resistance value of a resistance detector element is measured during the lapping process, and the measurement value is converted to the height of the MR element. It is a further object of the invention to provide a method of measuring both the variation in dimensions and the misalignment of the MR element and the resistance element, which become error factors, and an apparatus for carrying out the method. It is another object of the invention to provide a method of monitoring a MR element formation process by using the above-described method and apparatus, detecting a problem in the process, and modifying parameters of film deposition equipment and exposure equipment to eliminate the problem.
To achieve the above-described objects, the method of measuring the dimensions and alignment of a thin film magnetic head according to the present invention employs a magnetoresistance effect element and a resistance detector element for monitoring the lapping process, both of which are formed on a substrate and are illuminated with light emitted from a light source whose wavelength is 300 nm or less, preferably is 200 nm. An image is formed by imaging reflected light from the aforesaid elements, the image is converted to an image signal through photoconversion, and geometrical information of the above-described magnetoresistance effect element and the above-described resistance detector element for monitoring the lapping is detected from the aforesaid image signal.
Further, in accordance with the present invention, the above-described light is prescribed to be light having a wavelength of 248 nm, or of 266 nm, or of 213 nm.
Moreover, in accordance with the present invention, the above-described geometrical information includes the dimensions of the element or a measure of the alignment error of the element.
Furthermore, in accordance with the present invention, the above-described magnetoresistance effect element and the above-described resistance element for monitoring the lapping process have a structure wherein the elements are covered with end face protection films. Also, to achieve the above-described objects, the method for measuring the dimensions and alignment of a thin film magnetic head according to the invention employs a magnetoresistance effect element and a resistance detector element for monitoring the lapping process, both of which are formed on a substrate and are illuminated with light emitted from a light source whose wavelength is 300 nm or less, preferably is in the range of 200 nm. Reflected light from the elements is made to interfere with reference light, interference light thus formed (i.e. a combination of the diffracted light and the reference light) is imaged to form an image, this image is converted to an image signal through photoconversion, and geometrical information of the magnetoresistance effect element and the resistance detector element for monitoring the lapping is detected from this image signal.
Also, to achieve the above-described objects, the apparatus for measuring dimensions and alignment of the thin film magnetic head according to the invention comprises a light source; illuminating means for illuminating the magnetoresistance effect element and the resistance detector element for monitoring the lapping process, both of which are formed on a substrate, with light emitted from a light source whose wavelength is 300 nm or less, preferably in the vicinity of 200 nm; imaging means for imaging reflected light from this element; image pick up means for converting the image obtained by this imaging means to an image signal; and geometrical information detecting means for detecting geometrical information of the magnetoresistance effect element and the resistance detector element for monitoring the lapping.
Also, to achieve the above-described objects, the apparatus for measuring the dimensions and alignment of the thin film magnetic head according to the invention comprises a light source; illuminating means for illuminating the magnetoresistance effect element and the resistance detector element for monitoring the lapping, which are both formed on a substrate, with light whose wavelength is 300 nm or less, and preferably is in the vicinity of 200 nm; interfering means for making reflected light from the element interfere with reference light; imaging-means for imaging the interference light; image pick up means for converting an image obtained by this imaging means to an image signal; and geometrical information detecting means for detecting geometrical information of the magnetoresistance effect element and the resistance detector element for monitoring the lapping.